HP 2225D+ RAM failure/replacement


I have bought a 2225D+ printer that is not working. I have found the servicemanual, where there isn't but I am referring to the 2225C+ model.

The yellow led blinks twice, then a pause, then blinks continously.

All the voltages seem to be ok and the capacitors are ok too.

So, I have done the kernel troubleshooting and I have found a pulse on the cpu's pin #22==>RAM faulty.

The chip is labeled 1LK4-0001 and it should be a 256x4 bit... I think it is a custom chip that has not commercial equivalents neither similar chips with different pinouts...

But how it is addressed?? In a serial way via C/D and STR pins?
All the connections are on a bus wit the ROM chip, so I guess that RAM and ROM have their own addresses...

I can't buy another printer, neither a replacement expensive as gold.

By the way I think that this could be an interesting educational task... is there someone who can explain how this chip work, or where to find some docs, in order to try a replacement with a common commercial chip?



IIRC, it's a Saturn bus RAM chip. similar to what's used in the hybrid RAM modules of an HP-71B. The Saturn bus is documented in the HP-71B Hardware IDS (p/n 00071-90071), and in slightly less detail in "Custom CMOS Architecture for a Handheld Computer" by James P. Dickie in the July 1984 issue of Hewlett-Packard Journal.


hi luca,

assuming that eric is correct in saying that the RAM in your printer is SATURN-bus compatible, then it might be possible to hook a HP82420A 4kB memory module to the bus. there may be smaller memory modules out there, but i never came across one. no guarantee that this would work, though.

best regards,


Edited: 10 Sept 2013, 2:03 a.m.


so, I have read something into the very interesting "HP-71B Hardware IDS" doc.

What I was guessing, that was a way to reproduce the ram chip with a few discrete commercial components, is definitely not applicable.

The bus is really smart (respect what I was imagining) and thus I think that it will not accept a different ram module as told by Hans.

Probably a one-chip solution could be found with a microcontroller, but it is a task out of my skills :-/



Very interesting reply, Eric!

So, I think that I am going to read a lot. I hope to reach in understanding something.

Many thanks from Italy,

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